The present invention relates to a piezoelectric resonator, and a filter and an electronic component using the piezoelectric resonator, and more particularly, to a technique of effectively suppressing degradation of Q-value (impedance ratio=anti-resonance resistance/resonance resistance) in the piezoelectric resonator or the like.
In a piezoelectric resonator such as a crystal oscillator or the like using a BAW (Bulk Acoustic Wave) and a surface acoustic resonator using a SAW (Surface Acoustic Wave), a dielectric film such as SiO2 film or the like is added to the surface of the resonator. It has been a common practice to use the above technique for the purpose of improving temperature characteristics.
In general, the piezoelectric material has a negative temperature characteristic. When an SiO2 film having a positive temperature characteristic is then added to the piezoelectric material, the negative temperature characteristic of the piezoelectric material is canceled to obtain a favorable temperature characteristics. Further, frequency variation due to an effect of mass addition of SiO2 is used to allow the SiO2 film to serve as a trimming film, or to have a function of exhibiting environment resistance as a protective film.
Note that the technique of forming an SiO2 film onto the surface of the piezoelectric resonator is included, for example, in 81st Research Symposium Report (JAN. 30, 2003) of the 150th Japan Society for the Promotion of Science on Acoustic Wave Technology, entitled “Improvement in temperature characteristics of SMR-type piezoelectric thin film resonator”.
For example, in a conventional SMR (Solidly Mounted Resonator)-type piezoelectric resonator, as will later be described more in detail, there is inevitably a problem of degradation of Q-value while improving temperature characteristics of the piezoelectric resonator. Furthermore, the problem described above is relevant not only to the resonator, but also to a filter or an electronic component using the resonator.